A great deal of attention has been directed to the fabrication or manufacture of structural members that can withstand substantial structural loads and varying temperatures arising in the natural environment. In certain arid desert areas, average daily temperatures can reach 100.degree. F. or more. Most common structural members comprise a support structure using either metallic structures manufactured from aluminum, steel, stainless steel metallic fiber or other high strength metallic material. Further, large structural wooden members have been used in utility poles, bridge components, housing structures and other similar units. Such wooden and metallic structural members have had some substantial success.
Increasing attention has also been given to the manufacture of structural members from thermosetting and thermoplastic materials. Processing these materials offers improved manufacturing properties because of the ease of processing thermosetting and thermoplastic resins and combining those materials with reinforcing fibers.
Karino et al., U.S. Pat. No. 4,515,737 teach a process for producing a composite circular pipe. In the process, a thermoplastic resin pipe is formed using an extruder. The surface of the pipe is covered with a uniform layer comprising continuous fibrous reinforcing material impregnated with a thermosetting resin in its axial direction by a draw molding method, helically winding a continuous fibrous reinforcing material impregnated or not impregnated with a thermosetting resin uniformly on the initial resin fibrous reinforced layer. The Karino et al. material has a polyvinyl chloride pipe center and a first and second fibrous reinforcing layer. This process, using a wrapped layer, cannot be used for complex profile shapes.
Tanaka et al., U.S. Pat. No. 4,740,405 teach an extruded profile or frame member comprising a thermoplastic resin having reinforcing wires throughout the frame member joined using a thermosetting resin. The fibers are typically dispersed within the profile material.
Balazek et al., U.S. Pat. No. 4,938,823 teach a pultrusion/extrusion method in which continuous transit or longitudinal fiber or roving is coated with a thermosetting resin. The fibers are then combined with one or more fibrous reinforcing mats and pass through a second die to cure the thermosetting resin. This process forms a first profile. The surface of the substantially cured thermoset is then deformed and a thermoplastic resin is then applied to the deformed surface. The deformity in the thermosetting surface provides increased adhesion between the thermoset core and the thermoplastic exterior.
Hirao et al., U.S. Pat. No. 5,030,408 teach a method of forming a molded resin article combining both thermoplastic and thermosetting resins in a kneader extruder to form the article. The structures manufactured by agglomerating thermoplastic materials having a particle diameter of 0.05-0.5 .mu.m with particles of 10-1000 .mu.m diameter prior to kneading, then introducing the thermoplastic material into the kneader.
Strachan, U.S. Pat. No. 5,120,380 teaches a method of forming extruded profiles. In the process, cloth, preferably woven fiberglass is delivered by supply rolls and guided over the external profiled surface of a forming duct. The cloth is maintained in a shape by an air stream provided by a venturi blower. The air stream blows towards the die and at least partially diffuses through the cloth prior to the resin curing die. The air shaped cloth runs into a curing die where it is impregnated with a thermosetting resin. The thermosetting resin is cured into an extruded profile which is then withdrawn from the curing station using a pultrusion tractor device. The prior art shows a variety of thermoplastic/thermosetting composite materials that can be used as structural members. No one structure or method appears to be superior in forming structural members that can resist high structural loads in the varying temperatures found in the natural environment. Substantial need exists for improving the heat distortion temperature of composite structures.